Tissue-specific expression of a suicide gene for selective killing of neuroblastoma cells using a promoter region of the NCX gene.

The human NCX gene, a homologue of the murine neural crest homeobox (Ncx/Hox11L.1) gene whose expression is restricted to a subset of neural crest-derived tissues, was expressed in human neuroblastoma cells but not in other tumors or fibroblasts. A 4.5-kb genomic fragment in the 5'-flanking region of the NCX gene efficiently transcribed the fused luciferase reporter gene in human neuroblastoma cells but not in non-neuroblastoma cells. Sequential deletion of this regulatory region from the 5' side demonstrated that a 1.7-kb fragment upstream from the start codon retained the preferential promoter activity in neuroblastoma cells. The transcriptional activation by the NCX promoter was stronger than that by the SV40 T antigen promoter in human neuroblastoma cells. Transfection of neuroblastoma cells with the NCX promoter-linked herpes simplex virus-thymidine kinase (HSV-TK) gene increased their sensitivity to ganciclovir. The regulatory region of the NCX gene is thus useful for neuroblastoma-specific suicide gene therapy.